Mainframe Developer

InstantServe LLC; South Carolina; On-site; USD 90,000 - 120,000; Full time

Job summary

InstantServe LLC is seeking an experienced Mainframe Developer to design, build, and enhance a Composite Reservoir Accounts system within a z/OS environment. You will extend legacy COBOL applications, implement new account structures, and ensure accurate balances, settlements, and reconciliations.

Responsibilities include analyzing master files, developing end-to-end account types, and extending nightly/month-end processing.

Qualifications

• Double-entry accounting, accruals, value dating, and reconciliation.
• Month-end financial processing.
• COBOL copybooks, call chains, and batch job streams.
• T SO/ISPF, GDGs, SORT, and JCL utilities.

Responsibilities

• Analyze existing account master, posting, and balance-maintenance programs to determine changes for Composite Reservoir Accounts.
• Design and develop the new account type end-to-end, including master file structures, account opening/closing, linkage, sweep processing, allocation logic, and closing balance calculations.
• Develop and modify Enterprise COBOL programs, JCL, and batch processing workflows.
• Extend nightly and month-end processing cycles to support the new functionality within batch windows.
• Implement audit trails, exception reporting, and reconciliation controls for the new structure.
• Collaborate with accounting stakeholders to establish financial controls and audit requirements.
• Prepare test data, unit tests, regression test cases, and parallel-run comparisons against production outputs.
• Investigate and resolve discrepancies to ensure financial accuracy.
• Support implementation, account conversion, production deployment, and early-life production support.

Skills

COBOL

JCL

Batch processing

TSO/ISPF

GDGs

SORT

z/OS

Accounting

REXX

Python

Java

IBM MQ

z/OS Connect

REST integration

Tools

IBM MQ

z/OS Connect

REST integration

Job description

We are seeking an experienced Mainframe Developer – Composite Reservoir Accounts to support the development and enhancement of its existing mainframe accounting platform.

The project involves building a new Composite Reservoir Account (CRA) structure within an established z/OS environment. This pooled-account structure will consolidate balances from multiple subsidiary accounts into a single reservoir account and distribute funds based on predefined sweep and allocation rules.

The selected candidate will analyze, enhance, and extend existing legacy COBOL applications while ensuring that all account balances, transactions, settlements, accruals, reporting, and reconciliation processes remain accurate and consistent.

This role requires strong mainframe development expertise, financial accounting knowledge, and the ability to navigate complex, undocumented legacy systems. Accuracy, auditability, and financial data integrity are critical.

Key Responsibilities

• Analyze existing account master, posting, and balance-maintenance programs to determine the required changes for supporting Composite Reservoir Accounts.


• Design and develop the new account type end-to-end, including master file structures, account opening and closing, participant linkage, sweep/reverse-sweep processing, allocation logic, interest apportionment, and closing balance calculations.


• Develop and modify Enterprise COBOL programs, JCL, and batch processing workflows.


• Extend nightly and month-end processing cycles to support the new functionality while maintaining agreed batch processing windows.


• Implement audit trails, exception reporting, and reconciliation controls for the new account structure.


• Collaborate with accounting stakeholders to establish financial controls and audit requirements.


• Develop test data, unit tests, regression test cases, and parallel-run comparisons against existing production outputs.


• Investigate and resolve discrepancies to ensure complete financial accuracy.


• Support implementation, account conversion, production deployment, and early-life production support.


• Provide on-call support during initial production processing cycles.


• Prepare technical documentation, data-flow diagrams/notes, and operational runbooks.


• Follow formal production change management processes, including peer reviews and approved implementation plans.

Additional Required Knowledge:

• Double-entry accounting, accruals, value dating, and reconciliation.


• Month-end financial processing.


• COBOL copybooks, call chains, and batch job streams.


• TSO/ISPF, GDGs, SORT, and JCL utilities.

Preferred Skills

• Cash management, treasury applications, and account pooling.


• Financial sweep processing and cash concentration.


• CA-7 scheduling and batch operations.


• REXX, Python, or Java.


• IBM MQ, z/OS Connect, or REST integration.